linux-kernel - Re: [alsa-devel] [RFC PATCH 1/7] soundwire: Add sysfs support for master(s)

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Date:   Wed, 8 May 2019 11:42:15 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>, Vinod Koul <vkoul@...nel.org>
Cc:     alsa-devel@...a-project.org, tiwai@...e.de,
        linux-kernel@...r.kernel.org, liam.r.girdwood@...ux.intel.com,
        broonie@...nel.org, srinivas.kandagatla@...aro.org,
        jank@...ence.com, joe@...ches.com,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [RFC PATCH 1/7] soundwire: Add sysfs support for
 master(s)



On 5/8/19 4:16 AM, Greg KH wrote:
> On Wed, May 08, 2019 at 01:16:06PM +0530, Vinod Koul wrote:
>> On 07-05-19, 17:49, Pierre-Louis Bossart wrote:
>>>
>>>>> The model here is that Master device is PCI or Platform device and then
>>>>> creates a bus instance which has soundwire slave devices.
>>>>>
>>>>> So for any attribute on Master device (which has properties as well and
>>>>> representation in sysfs), device specfic struct (PCI/platfrom doesn't
>>>>> help). For slave that is not a problem as sdw_slave structure takes care
>>>>> if that.
>>>>>
>>>>> So, the solution was to create the psedo sdw_master device for the
>>>>> representation and have device-specific structure.
>>>>
>>>> Ok, much like the "USB host controller" type device.  That's fine, make
>>>> such a device, add it to your bus, and set the type correctly.  And keep
>>>> a pointer to that structure in your device-specific structure if you
>>>> really need to get to anything in it.
>>>
>>> humm, you lost me on the last sentence. Did you mean using
>>> set_drv/platform_data during the init and retrieving the bus information
>>> with get_drv/platform_data as needed later? Or something else I badly need
>>> to learn?
>>
>> IIUC Greg meant we should represent a soundwire master device type and
>> use that here. Just like we have soundwire slave device type. Something
>> like:
>>
>> struct sdw_master {
>>          struct device dev;
>>          struct sdw_master_prop *prop;
>>          ...
>> };
>>
>> In show function you get master from dev (container of) and then use
>> that to access the master properties. So int.sdw.0 can be of this type.
> 
> Yes, you need to represent the master device type if you are going to be
> having an internal representation of it.

Humm, confused...In the existing code bus and master are synonyms, see 
e.g. following code excerpts:

  * sdw_add_bus_master() - add a bus Master instance
  * @bus: bus instance
  *
  * Initializes the bus instance, read properties and create child
  * devices.

struct sdw_bus {
	struct device *dev; <<< pointer here
	unsigned int link_id;
	struct list_head slaves;
	DECLARE_BITMAP(assigned, SDW_MAX_DEVICES);
	struct mutex bus_lock;
	struct mutex msg_lock;
	const struct sdw_master_ops *ops;
	const struct sdw_master_port_ops *port_ops;
	struct sdw_bus_params params;
	struct sdw_master_prop prop;

The existing code creates a platform_device in 
drivers/soundwire/intel_init.c, and it's assigned by the following code:

static int intel_probe(struct platform_device *pdev)
{
	struct sdw_cdns_stream_config config;
	struct sdw_intel *sdw;
	int ret;

	sdw = devm_kzalloc(&pdev->dev, sizeof(*sdw), GFP_KERNEL);
[snip]
	sdw->cdns.dev = &pdev->dev;
	sdw->cdns.bus.dev = &pdev->dev;

I really don't see what you are hinting at, sorry, unless we are talking 
about major surgery in the code.